1. Field of the Invention
The present invention is concerned generally with coating compositions and, more particularly, relates to thermosettable powder coating compositions comprising a polyester resin as a major component thereof.
2. Description of the Prior Art
In U.S. Pat. No. 3,842,021 to Grant et al there are disclosed polyester resin compositions suitable for powder coating. The resin is derived from a dicarboxylic acid component, at least 50 mole percent of which is 1,4-benzenedicarboxylic acid (terephthalic acid), a glycol component, at least 50 mole percent of which is 2,2-dimethyl-1,3-propanediol (neopentyl glycol), and from about 2 to 10 mole percent of a polyol containing 4 to 16 carbon atoms and having at least 3 primary hydroxyl groups. It is taught that, when such resin compositions have a glass transition temperature of at least 60.degree. C., one may use them to formulate a powder coating composition which is non-caking, friable and free-flowing at ambient conditions.
U.S. Pat. No. 4,054,681 to Bruning et al teaches a powder coating composition which is based on a partially crystalline powder of a polyester condensation product of an acid component, at least 60 mole percent of which is 1,4-benzenedicarboxylic acid, and a diol component, at least 50 mole percent of which is 1,4-butanediol, and which has a glass transition temperature of between 20.degree. C. and 50.degree. C. The disclosed compositions are said to readily adhere even to smooth metal surfaces such that they do not become delaminated and are stable in storage.